This invention relates to a method for making abrasive agglomerate particles comprising a binder and abrasive grains. The abrasive agglomerate particles made by the present invention can be used in abrasive products such as, for example, coated abrasives, bonded abrasives and nonwoven abrasives.
In the abrasives industry, conventional coated abrasive articles typically consist of a layer of abrasive grains adhered to a backing. When abrasive grains are worn the resulting abrasive article is rendered inoperable and the backing, one of the more expensive components of the coated abrasive article, must be disposed of before it has worn out.
Many attempts have been made to distribute the abrasive grains on the backing in such a manner so that the abrasive grains are better utilized, in order to extend the useful life of the coated abrasive article. By extending the life of the coated abrasive article, fewer belt or disc changes are required, thereby saving time and reducing labor costs. Merely depositing a thick layer of abrasive grains on the backing will not solve the problem, because grains lying below the topmost grains are not likely to be used.
Several methods whereby abrasive grains can be distributed in a coated abrasive article in such a way as to prolong the life of the article are known. One such way involves incorporating abrasive agglomerate particles in the coated abrasive article. Abrasive agglomerate particles consist of abrasive grains bonded together by means of a binder to form a mass. The use of abrasive agglomerate particles with the surface having random shapes and sizes makes it difficult to predictably control the quantity of abrasive grains that come into contact of a workpiece. For this reason, it would be desirable to have an economical way to prepare abrasive agglomerate particles.
The present invention involves a method for making abrasive agglomerate particles from a composition comprising at least a radiation curable binder and abrasive grains. In a preferred embodiment, the binder is radiation curable and polymerizable.
The method of the present invention involves forming abrasive agglomerate precursor particles and curing them. In a preferred embodiment, the first step involves forcing the binder precursor and abrasive grains through a perforated substrate to form abrasive agglomerate precursor particles. Next, the abrasive agglomerate precursor particles are separated from the perforated substrate and irradiated with radiation energy to provide abrasive agglomerate particles. In a preferred embodiment, the method of forcing, separating and irradiating steps are spatially oriented in a vertical and consecutive manner, and are performed in a sequential and continuous manner. Preferably, the abrasive agglomerate particles are solidified and handleable after the irradiation step and before being collected.
Binder precursors of the present invention include thermal and radiation curable binders. Preferable binder precursors comprise epoxy resins, acrylated urethane resins, acrylated epoxy resins, ethylenically unsaturated resins, aminoplast resins having pendant unsaturated carbonyl groups, isocyanurate derivatives having at least one pendant acrylate group, isocyanate derivatives having at least one pendant acrylate group or combinations thereof. Preferred abrasive grains comprise fused aluminum oxide, ceramic aluminum oxide, white fused aluminum oxide, heat treated aluminum oxide, silica, silicon carbide, green silicon carbide, alumina zirconia, diamond, ceria, cubic boron nitride, garnet, tripoli or combinations thereof. In one embodiment, the abrasive grains are from 5% to 95%, by weight, of the agglomerate composition. In a preferred embodiment, the abrasive grains are from 40% to 95%, by weight, of the agglomerate composition.
The agglomerate composition of binder precursor and abrasive grains preferably has a high viscosity. In the most preferred embodiment, the composition is formed from a binder precursor that is 100% solids (i.e. no volatile solvents at process temperature).
Methods of forcing the binder precursor and abrasive grains through a perforated substrate comprise extrusion, milling, calendering or combinations thereof. In a preferred embodiment, the method of forcing is provided by a size reduction machine, manufactured by Quadro Engineering Incorporated.
In one embodiment, the abrasive agglomerate precursor particles are irradiated by being passed through a first curing zone which contains a radiation source. Preferred sources of radiation comprise electron beam, ultraviolet light, visible light, laser light or combinations thereof. In another embodiment, the abrasive agglomerate particles are passed through a second curing zone to be further cured. Preferred energy sources in the second curing zone comprise thermal, electron beam, ultraviolet light, visible light, laser light, microwave or combinations thereof.
In a preferred embodiment, the abrasive agglomerate particles are filamentary shaped and have a length ranging from about 100 to about 5000 micrometers. Most preferably, the filamentary shaped abrasive agglomerate particles range in length from about 200 to about 1000 micrometers. In one embodiment, the abrasive agglomerate particles are reduced in size after either the first irradiation step or after being passed through the second curing zone. The preferred method of size reducing is with the size reduction machine manufactured by Quadro Engineering Incorporated.
In one embodiment, the cross-sectional shapes of the agglomerate particles comprise circles, polygons or combinations thereof. Preferably, the cross-sectional shape is constant.
In one embodiment, the agglomerate particles comprise an inorganic binder precursor additive. Preferably, the inorganic binder precursor additive comprises glass powder, frits, clay, fluxing minerals, silica sols, or combinations thereof.
In one embodiment, the abrasive agglomerate precursor particles comprise a modifying additive. Preferably, the modifying additive comprises coupling agents, grinding aids, fillers, surfactants or combinations thereof.
The abrasive agglomerate particles of the invention may be incorporated into conventional abrasive articles (e.g. bonded abrasives, coated abrasives and nonwoven abrasives). Abrasive articles, with the abrasive agglomerate particles of the present invention, have exhibited long life, high cut rates and good surface finishes.